This research proposal is a continuation of my present work and is directly related to the field of "Local Neuronal Interactions", a field in which the Fundamental Neurosciences Program (FNP) of NINCDS is presently encouraging more research. Studies in this laboratory on both the cat and the primate lumbosacral spinal cord show that the marginal and substantia gelatinosa (SG) layers, Laminae I and II respectively, are composed of a variety of neuronal cell types having a wide range of dendritic configurations and specializations. In spite of the diversity, a repeating pattern of cell types is apparent to the extent that a functional correlation with neuronal configuration is probable. Focusing on this premise, the objective of this proposal is to examine the synaptic input to specific neuronal cell types within the marginal and SG layers of the cat and determine to what extent, if any, the morphological variations of these neurons reflect variations in the types and distribution of inputs received. Particular attention will be directed to the types of input to specialized dendritic regions, e.g., spines, dendritic appendages, axon-like processes etc., since the number and distribution of these specializations often characterize the cell morphologically. Two major inputs to the marginal and SG layers will be examined: 1) primary afferents and 2) descending (dorsolateral funicular) afferents. Primary afferent lesions performed by either dorsal rhizotomies or peripheral axotomies, and descending afferent lesions effected by hemisection of the spinal cord will allow for the ultrastructural identification of early degenerating synaptic terminals in the marginal and SG layers. The exact relationship of these descending inputs to specific cell types will be determined by serial section and ultrastructural examination of Golgi impregnated-"gold toned" neurons in the marginal and SG layers.